For example, bottles are successively manufactured via a plurality of sections of bottle making machines in a bottle manufacturing plant. While being conveyed to a final stage of wrapping process, the bottles pass through inspection lines, and inspection for the presence or absence of defects and so forth are carried out. As a bottle inspection device installed in this type of inspection line, a plurality of inspection stations is arranged around a star wheel. A star wheel 8 illustrated in FIG. 17 is provided with a plurality of recesses 80 on the outer peripheral surface, and a bottle 10 introduced into each recess 80 is sequentially fed to each inspection station in accordance with the intermittent rotation of the star wheel 8. In an inspection station for inspecting the wall thickness of the bottle 10, the bottle 10 to be inspected is supported at the rotational center on the upper surface of a support table, and by axially rotating the bottle 10 around the central axis using a rotary drive mechanism, the wall thickness of the bottle 10 is measured over the entire periphery thereof, and thus the quality of the bottle 10 is determined.
An electrostatic capacity detector 9 is used as this type of wall thickness inspection device, for detecting the electrostatic capacity between the electrode pattern of a measuring electrode and the electrode pattern of an earth electrode with a sensor unit 90 brought into contact with the surface of the bottle 10 (for example, refer to a patent document 1). The electrostatic capacity detector 9 is provided with an elastic body 91 which pushes the sensor unit 90 toward the surface of the bottle 10, and thus even if the bottle 10 is vibrated, the elastic body 91 absorbs the vibration to stably maintain the contact state between the sensor unit 90 and the surface of the bottle 10.
The sensor unit 90 is formed by bonding an electrode sheet 93 made of synthetic resin, which has an electrode pattern formed thereon, to the surface of a belt-like attachment substrate 92 curved over the entire length. An electrostatic capacity of a portion of the bottle 10 with which the sensor unit 90 is brought into contact is detected between the electrode pattern of the measuring electrode and the electrode pattern of the earth electrode, while the detection output of the electrostatic capacity is introduced into an arithmetic and control unit (not shown) and converted into a wall thickness.